Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/10—Controlling the intensity of the light
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/40—Details of LED load circuits
  • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
  • H05B45/48—Details of LED load circuits with an active control inside an LED matrix having LEDs organised in strings and incorporating parallel shunting devices
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B44/00—Circuit arrangements for operating electroluminescent light sources
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/395—Linear regulators
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/40—Details of LED load circuits
  • H05B45/44—Details of LED load circuits with an active control inside an LED matrix
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
  • F21Y2105/00—Planar light sources
  • F21Y2105/10—Planar light sources comprising a two-dimensional array of point-like light-generating elements
  • F21Y2105/12—Planar light sources comprising a two-dimensional array of point-like light-generating elements characterised by the geometrical disposition of the light-generating elements, e.g. arranging light-generating elements in differing patterns or densities
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
  • F21Y2115/00—Light-generating elements of semiconductor light sources
  • F21Y2115/10—Light-emitting diodes [LED]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
  • Y02B20/30—Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Definitions

• This invention relates to an LED arrangement and LED driving method, in particular which makes use of a linear tapped driver architecture.
• the available space for an LED driver has limited many retrofit applications for LED lamps, such as a tubular LED lamp.
• the traditional LED architecture and driver topology for tubular LEDs requires a driver space much larger than the space that the existing tube dimensions (e.g. a T5 tube) can offer.
• a tapped linear driver design is therefore considered as a good alternative solution for applications with space constraints, since it requires much smaller power components and enables the driver size to be minimized.
• a problem with the use of a tapped linear driver is that different sets of LEDs are turned on at different times and for different duration, for example at different interval of a mains cycle. This gives rise to a different light distribution and output intensity for the different sets.
• a tapped linear driver is disclosed in US8896235B1.
• the sets are turned on in a monotonically accumulative manner namely a first set is turned; then a second set is turned on together with the first set; and then a third set is turned on together with the first and the second set.
• LEDs in the set that is turned on for longest duration is placed at the center.
• Another prior art DE202013000064U1 shows a non-mo notonically turning on order wherein the tapped sets in tapped linear driver can be turned on and turned off many time when the voltage increases from zero crossing to the peak.
• some set is configured to provide more light output to a working plane while some set is configured to provide less light output for indirect lighting.
• a LED arrangement placed over a light output surface comprising:
• said first group of LEDs is adapted to be kept turning on and the second group of LEDs is adapted to be bypassed when the mains input is below a first threshold, and said first group of LEDs and the second group of LEDs are adapted to be kept turning on when the mains input is above the first threshold, and
• the total light output density for the LEDs of the second group per unit area of the light output surface is greater than the total light output density for the LEDs of the first group per unit area of the light output surface, wherein a fraction of a light emitting surface of the second group of LEDs to a second area of the light output surface occupied in a macro view by the second group of LEDs, is larger than a fraction of a light emitting surface of the first group of LEDs to a first area of the light output surface occupied in a macro view by the first group of LEDs.
• This arrangement for example provides a tapped linear AC LED driver.
• the groups of LEDs may be driven together or else only one may be driven when the input voltage is low.
• each group of LEDs may have its own current source arrangement.
• a first current is driven through only the first group of LEDs if the rectified mains voltage is only sufficient to operate the first group of LEDs.
• a second current is driven through the series connection of the first and second groups of LEDs.
• This is the general arrangement of a tapped linear driver. It means that some LEDs are on for a different duration than others.
• the time-average light output intensity per area of the light output surface is made closer to the average light output intensity per area of the first group. In other words, the luminous emittance (lm/m 2 ) over time may be made more uniform.
• light output density is meant the product of the light output intensity per unit area (candelas/m 2 ) of an LED chip multiplied by the light emitting surface of that LED chip. Thus, it is a measure of the total light intensity output of an LED chip or an
• the "total light output density" is this measure for all LEDs of a group.
• the total light output density ... per unit area of the light output surface is meant the total effective light output intensity normalized to the area of the light output surface, in particular the area of the light output surface which is occupied in a macro view by that group of LEDs. In other words, it is the surface throughout which that group of LEDs is distributed and seen as providing illumination. It does not mean the small footprint of the LED on the light output surface.
• the first LED arrangement will occupy an overall first area of the light output surface, but only a portion of this first area which is LED chips is actually light emitting because the light output surface further includes the spaces between LED chips. Assuming the same output intensity per unit area of the light emitting surface of LED, the size of this portion relative to the overall first area is what is important.
• the combination of the overall areas of the different groups of LEDs makes up the full light output surface (part of which is light emitting surfaces namely the LED chip/footprint and other parts of which are spaces between the light emitting surfaces).
• the LED arrangement may further comprise:
• At least one further group of LEDs in series with said first group and said second group, wherein said second and third groups of LEDs is adapted to be bypassed when the mains input is below the first threshold, and said third group of LEDs is adapted to be bypassed when the mains input is above said first threshold and below a second threshold, said first group of LEDs, the second group of LEDs and at least one further group of LEDs are adapted to be kept turning on when the mains input is above the second threshold,
• the total light output density for the LEDs of the or each further group per unit area of said light output surface is greater than the total light output density for the LEDs of the preceding group per unit area of said light output surface, wherein a fraction of a light emitting surface of the third group of LEDs to a third area of the light output surface occupied in a macro view by the third group of LEDs, is larger than the fraction of te light emitting surface of the second group of LEDs to the second area of the light output surface occupied in a macro view by the second group of LEDs.
• the densities are for example selected such that the total light output amount for the LEDs of the second group per unit area and per unit time is substantially equal to the total light output amount for the LEDs of the first group per unit area and per unit time.
• the intensity per unit area i.e. the emittance
• the intensity per unit area remains substantially constant as the driver cycles through the different combinations of groups of LEDs.
• the light output amount of the second group of LEDs per unit area of the light output surface, and of any further groups is between 0.9 and 1.1 times the light output of the LEDs of the first group per unit area of the light output surface, more preferably between 0.95 and 1.05 times.
• the different LED groups are made to emit light with roughly the same intensity per unit area, i.e. the same visible output brightness over area when averaged over time.
• the visible light is uniform throughout the light output surface, and the drawback of the tapped linear driver is compensated.
• the LED chips of the LEDs of the second group and any further group may each have a larger size than that of the LEDs of the preceding group.
• the number of LEDs in each group per unit area of the light output surface may be the same, namely with the same pitch.
• This provides a first way of making the time-average intensity closer, by having larger LEDs when those LEDs are turned on for a shorter time.
• the size of the overall LED package that encapsulates the LED chips may be the same or different.
• LED packages of a given size may have LED chips of different size. This means the footprint for all LED packages can be made the same.
• the number of LEDs of the second group and any further group per unit area of the light output surface is larger than that of the LEDs of the preceding group, and the size of LEDs in each group is the same, namely using a different pitch.
• This provides a second way of differentiating the output density per unit area and in turn making the time-average intensity closer, by having more closely packed LEDs when those LEDs are turned on for a shorter time.
• the above first and second approaches may also be combined. In one such combination, larger LED chips are more closely placed with respect to smaller LED chips.
• the first group may be regulated by a first current source arrangement when the mains input is below a first threshold, and the first group and second group may be regulated by a second current source arrangement when the mains input is above said first threshold, wherein the second current source arrangement and any further current source arrangement drives a larger current than the preceding current source arrangement.
• the light output density of each group per unit area of the light output surface is adapted to compensate the difference in light output amount of each group when driven by the current regulated by the first current source arrangement and the later current source arrangement or arrangements during a given mains cycle or rectified mains cycle.
• the mains cycle is 20ms and a rectified mains cycle is 10ms.
• Each group of LEDs may be associated with a current source and a control switch, and the driver further comprises a driver for controlling the control switches.
• the driver is preferably adapted to control the control switches with a non-overlapping sequence.
• one current source is turned on at a time, based on the level of the rectified mains input.
• Examples in accordance with another aspect of the invention provide a method of controlling an LED arrangement, comprising:
• the total light output density for the LEDs of the second group per unit area of the light output surface is greater than the total light output density for the LEDs of the first group per unit area of the light output surface.
• the method may further comprise: during one or more further portions of the mains input cycle above a further threshold voltage, keeping driving a respective further current through a respective further group of LEDs and through the preceding groups of LEDs,
• the total light output density for the LEDs of the or each further group per unit area of the light output surface is greater than the total light output density area for the LEDs of the preceding group per unit area of the light output surface, wherein a fraction of a light emitting surface of the further group of LEDs to a further area of the light output surface occupied in a macro view by the further group of LEDs, is larger than the fraction of the light emitting surface of the preceding group of LEDs to the preceding area of the light output surface occupied in a macro view by the preceding group of LEDs.
• the light output amount of the second group of LEDs per unit area of the light output surface, and of any further groups may be between 0.9 and 1.1 times the light output of the LEDs of the first group per unit area of the light output surface, more preferably between 0.95 and 1.05 times.
• Control switches which each couple a current source to a respective group of
• LEDs may be operated with a non-overlapping sequence.
• Figure 1 shows a known LED arrangement with a linear tapped LED driver
• Figure 2 shows waveforms to explain the operation of the LED arrangement of Figure 1;
• Figure 3 shows a first example of a LED arrangement in accordance with the invention, wherein the pitch is different
• Figure 4 shows a second example of a LED arrangement in accordance with the invention, wherein the LED chip size is different.
• Figure 5 shows a third example of a LED arrangement in accordance with the invention wherein the LED chip size is different but the LED package size is the same.
• the invention provides an LED arrangement which uses a tapped driver driven by a rectified mains input.
• a light output surface which may be the tubular surface of a tubular LED lamp that provides the illumination.
• the second group of LEDs is bypassed when the input voltage is less than a certain threshold while the first group is still turned on.
• the total light output density for the LEDs of the second group (which are turned on for less of the mains cycle) per unit area of the light output surface is greater than the total light output density for the LEDs of the first group per unit area of the light output surface. This means the light output density per unit area when averaged over time is made more consistent between the two (or more) groups of LEDs.
• Figure 1 shows a known tapped linear LED driver architecture which may be used to implement the LED arrangement of the invention.
• the circuit of Figure 1 comprises a mains input 10 which is provided to a diode bridge rectifier 12.
• the rectified output Vb is provided to three strings of LEDs.
• a first string 14 is between the rectified output and a first current source Icsl which sinks to ground.
• a second string 16 is in series with the first string 14 between the rectified output and a second current source Ics2 which sinks to ground.
• the first current source Icsl connects to the junction between the first and second LED strings 14,16.
• a third string 18 is in series with the first and second strings 12,14 between the rectified output and a third current source Ics3 which sinks to ground.
• the second current source Ics2 connects to the junction between the second and third LED strings 16,18.
• Each current source has an associated series control switch SI, S2, S3.
• the three switches SI, S2, S3 are controlled according to the mains input voltage.
• the rectified mains voltage Vb is higher than a first threshold that is the forward voltage of LED string 14 but lower than a second threshold that is the sum of forward voltage of LED strings 14 and 16
• SI is at the "on” state
• S2 and S3 are at the "off state. Only LED string 14 is turned on.
• the architecture may be scaled to four or more groups, or be scaled to two groups.
• VLEDstringl is the voltage needed to drive current through the string 14 alone.
• VLEDstring2 is the voltage needed to drive current through the series combination of strings 14 and 16.
• VLEDstring3 is the voltage needed to drive current through the series combination of all three strings.
• the different groups of LEDs may for example be different color LEDs or all are white.
• the on-time for each group of LEDs is different. If they are driven with the same current, the average light output in a given time is equal to the average power on time. The consequence is that total lumen outputs for the LEDs in different groups, and therefore at different segment locations of the light emitting surface, are varied. This leads to unwelcome light uniformity changes if the same LED distribution is provided in the overall light output surface as in traditional linear LED light sources.
• One way to solve this problem is blending/interleaving the LEDs of different groups but this needs complex wiring.
• the invention is based on redefining the distribution of LEDs of the light output surface (e.g. strip) to be suitable for a tapped linear driver.
• the invention may be applied to the LED arrangement as shown in Figure 1 and driven according to the drive scheme shown in Figure 2.
• the invention relates to the physical layout of LED chips on a shared light output surface.
• a first example is shown in Figure 3.
• the three LED strings are on a common light output surface 20 which has light emitting surfaces (the LED chips) and non-light emitting surfaces (the spaces between the LED chips). With a constant current on LEDs, the total output power (light) on the three LED strings in a cycle stays at a ratio of about 34: 16:6. Therefore the area for the three strings shall keep the same ratio to provide the same light output density.
• the total light output density for the LEDs of the second group per unit area of the light output surface 20B is greater than the total light output density for the LEDs of the first group per unit area of the light output surface 20A This means that for the part of the light output surface 20B attributable to the second group 16, the relative area of the light emitting surfaces is greater than for the first group 14 (assuming the same light output intensity per unit of light emitting surface for simplicity - although this is not essential as explained below). There may be more LEDs in the first group (as in the example shown) so that the total light emitting surface of the first group may in fact be larger.
• the light emitting surface per amount of surface area occupied by the LED group (as shown by dotted rectangles) is larger for the second group.
• the light output density per unit area of light output surface occupied by the second group is greater.
• the LEDs are denser (i.e. closer together) along the tubular axis for the second group than the first group.
• the desired uniformity is achieved by placing identical LEDs (wioth the same LED size) closer together in the area allocated to the LEDs of the second group.
• the total light output density is larger for the second group than for the first group.
• the second group has 4 units of light emitting surface (namely LEDs) concentrated into a smaller space than four corresponding units of the first group 14.
• a larger fraction of the area 20B of the second group 16 is light emitting.
• the third group 18 has three LEDs which occupy a smaller area than three of the LEDs from the first or second groups. Put another way, the spacing between LEDs of the first group is larger than the spacing between LEDs of the second group, and the spacing between LEDs of the second group is larger than the spacing of the LEDs of the third group.
• the time-average light output intensity can be made the same for all groups.
• the luminous emittance (lm/m 2 ) when averaged over time may be made constant.
• the total light output amount for the LEDs of the second group 16 per unit area and per unit time is substantially equal to the total light output amount for the LEDs of the first group 14 per unit area and per unit time.
• the first group 14 will in this example be driven at three different light intensities as shown in Figure 2, whereas the second group 16 will be driven at two different light intensities.
• the intensity per unit area i.e. the emittance
• the intensity per unit area can be made the same for the different groups 14, 16, 18 when averaged over an integer number of cycles of the mains input.
• the human eye will see the average light intensity, this means the light output intensity will look the same at all locations on the light output surface namely along the tube lamp, even if the different groups are spatially separated.
• the time-averaged light output amount of the second group of LEDs per unit area of the light output surface, and of any further groups may be between 0.9 and 1.1 times the time-averaged light output of the LEDs of the first group per unit area of the light output surface, more preferably between 0.95 and 1.05 times.
• the different LED groups are made to emit light with roughly the same intensity per unit area, i.e. the same visible output brightness over area when averaged over time.
• Figure 4 shows a second example and Figure 5 shows a third example.
• the LED pitch size is kept the same and the total LED chip size (namely the light emitting surface) of the LEDs in the different groups is different.
• the first group 14 has the smallest area LED chips, the second group has larger area LED chips and the third group has the largest area LED chips.
• LED packages change size according to the chip size.
• the overall LED packages have the same size but contain different sizes of light emitting chips.
• the LED chip of the LEDs of the second group and any further group each have a larger size than that of the LEDs of the preceding group.
• the number of LEDs in each group per unit area of the light output surface, namely the pitch size may be the same. This means they are uniformly distributed (in terms of the pitch between centres).
• the drive current may be larger when there are more
• the light output density of each group per unit area of the light output surface also compensates for the difference in light output amount of each group when driven by the various different currents which are used by the LED driver.
• Figures 1 and 2 show an example of tapped linear driver in which each group of LEDs is associated with a current source and a control switch, and the driver comprises a driver for controlling the control switches.
• the driver controls the control switches with a non-overlapping sequence.
• alternative current source arrangements are possible, for example a single controllable current source may be controlled in synchronism with the switching of LED strings into circuit.
• the LED strings may for example all be in series and each be bypassed by a respective bypass switch in parallel with the LED string.
• a single current source may then controlled to drive current through all strings. Different LED strings are bypassed at different times, and the current level is controlled in dependence on the switching state of the bypass switches.
• each group comprising only one series string of LEDs is simply for ease of explanation.
• Each group may comprise many parallel strings of LEDs, with a current selected accordingly.
• High voltage LEDs have been given as an example above, but there may of course be a larger number of lower voltage LEDs in each string.
• the lumen per cycle for each group of LEDs is calculated based on the drive current waveform applied to the LEDs for the full mains cycle, taking account of the different currents and timing of operation.

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